"These unique fossils provide irrefutable evidence that a member of the rail family colonized the atoll, most likely from Madagascar, and became flightless independently on each occasion.

"Fossil evidence presented here is unique for rails, and epitomizes the ability of these birds to successfully colonize isolated islands and evolve flightlessness on multiple occasions."

That seems like a step back, doesn't it?

Iterative evolution is when the same traits appear from a common ancestor at different times in history.

Think of it as a controlled experiment for evolution. Given the same environmental factors on a specific species, what new traits appear?

The birds lose their ability to fly since the atoll has no natural predators and an abundance of resources. However, fossil evidence shows this ending poorly for the flightless birds.

When the sub-species appeared previously 136,000 years ago, the island happened to flood, killing off the original flightless variant.

Co-author of the study, Professor David Martill said,

"Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion."

Despite the depictions in pop culture, evolution doesn't always add new abilities, nor is it moving in a specific direction to make a species more human-like.

What we're saying is nature is crazy.

Rather, natural selection favors whatever helps the species survive, including instances of conserving energy. Without predators or competing mammals, the need to fly is wasted energy.

Professor Martill said,

"We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently.

"Only on Aldabra, which has the oldest paleontological record of any oceanic island within the Indian Ocean region, is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonization events."